1. Field of the Invention
This invention relates to a process for producing a toner used in image forming processes, such as electrophotography, electrostatic recording and electrostatic printing, and to an apparatus for modifying surfaces of toner particles.
2. Related Background Art
In general, processes for producing toner particles may include pulverization and polymerization. Toner particles produced by pulverization are, under existing circumstances, advantageous in that they can be produced at a lower cost than those produced by the polymerization and are also at present widely used in toners for copying machines and printers. In the case when toner particles are produced by pulverization, a binder resin, a colorant, and so forth, are mixed in stated quantities, the mixture obtained is melt-kneaded, the kneaded product obtained is cooled, the kneaded product, thus cooled to solidify, is pulverized, the pulverized product obtained is classified to obtain toner particles having a stated particle size distribution, and a fluidity improver is externally added to the toner particles obtained, to produce a toner.
In recent years, there has been a demand for copying machines and printers that can achieve high image quality, energy savings, environmental adaptation, and so forth. For this reason, there is a shift to toners, in their technical concept, made of spherical toner particles to achieve high transfer efficiency and reduce waste toners. A method of making toner particles spherical by mechanical pulverization is proposed in Japanese Patent Application Laid-open No. H09-85741. Also, a method of making toner particles spherical by the action of hot air is proposed in Japanese Patent Application Laid-open No. 2000-29241. However, mechanical pulverization cannot provide sufficiently spherical toner particles. Also, if the process utilizes hot air, wax begins to melt when toner particles are incorporated with wax, which makes it difficult to control surface properties of toner particles and results in a problem of the quality stability of toner particles.
To cope with these issues, Japanese Patent Application Laid-open No. 2002-233787 proposes an apparatus for modifying surfaces of toner particles that also enables high-performance surface treatment and removal of fine powder. However, it is desirable to improve upon this surface modifying apparatus, because fine-powder removal efficiency, which is called classification efficiency, tends to decrease and image fog tends to occur when a high degree of spherical treatment is maintained.